Internal combustion engine



' July 21, 1936. A. ZOLLER INTERNAL COMBUSTION ENGINE Filed Jan. 11, 193-3 Ill/Ill Jill!!! I 0 l M w X F 5, /l/l/lll/l/ ///////////lllll/// 1 Y \\\\\\\\i a Patented July 21, 1936 fUNlTE D STATES PATENT. OFFICE Application January 11, 1933, Serial No. 651,189 In Germany January 12, 1932 6 Claims.

This invention has for its object improvements in and relating to two stroke internal combustion engines.

In two stroke internal combustion engines in which the gases of the combustion are expelled out of the cylinders through the fresh charge of mixture introduced into the cylinders, losses are frequently caused by the fact that the exhaust ports are not yet closed when the burnt gases 10 have already been expelled out of the cylinders. In such case parts of the fresh mixture escape into the atmosphere without'having been burnt, i. e. without having been utilized, until a further escape of the fresh mixture is prevented by the closure of the exhaust ports.

Thus sucha two stroke internal combustion engine works with the minimum of losses when the exhaust ports are closed by the control gear at the time when all the burnt gases have been expelled out of the cylinders and when the fresh mixture just reaches the exhaust ports.

, The time which elapses or the angle which the crank describes from the beginning of the admission to the moment where the fresh mixture reaches the exhaust ports is a function of the scavenging "or charging pressure, which itself is a iunction'oi the size of the admission and exhaust ports, on the one hand, as well as of the dimensions of the cylinders and, on the other hand, of the pressure lasting on the mixture before the latter enters the cylinder or cylinders through the admission ports. Another dependency relation is present betweenthe size of the admission sections and the time ,or the crank 3:, angle during which the admission ports must still remain open after the closure of the exhaust ports if an overpressure of the charge in the cylinder equal or corresponding to the overpres: sure existing in advance of the admission ports 40 before the beginning of the compression is" desired.

with the known arrangements with predeter- -mined sizes for the exhaust and admission ports the optimum can be obtained only for a predetermined speed or only for a very small speed range of the engine, because when the speed'increases the so-called time-sections, that is the products of time and size of the sections of the exhaust or admission ports which are momentarily free become smaller. Thus, if the sections of the portsare very large, i. e. if they are designed for great speeds, fresh mixture will escape through the exhaust ports at small speeds, thus producing losses of mixture, the engine having then a relatively small power and working uneconomically 'a' larger supercharging in the range of small speeds. On the other hand,

if the sections of the admission and exhaust ports are small, the engine being then designed in order to work with a high commercial emciency at small speeds, the charge resistances will be 5 very high at high speeds with this result that the pressure of the charge or the weight of the charge in the engine cylinder will be small or that the power consumption of the charging pump will be very high.

Arrangements with control gears which are controllable during the operation and through which the above mentioned inconveniences may be avoided. are. less reliable in operation and more expensive than the normal control gears 15 of simpler design.

One object of the invention is toavoid the inconveniences of the known control gears which are uncontrollable in operation for two stroke internal combustion engines, as much as possible, 20 and more particularly to provide in a so-called U-shaped engine, i. e. an engine of the known type with twin cylinders connected together through a common combustion chamber, the one of which comprising the admission ports and the 25 other the exhaust ports, large or normal timesections'without substantial losses of fresh gases at small speeds and without subtantially larger losses of charge at high speeds.

' Anotherobject of the invention is to provide 30 angle in an engine of the above mentioned kind and in spite of this a closure of theexhaust ports in due time and consequently an early beginning of the compres- 35 sion.

A further object-of the invention is to avoid the inconveniences of engines of the above men'- tioned kind by means oi connecting rods of diflerent lengths for the two pistons of the twin cylinders, but with the aid of equal crank circles for 4 the two connecting rods with the same spacing of the two cylinder axes from the crank shaft Still another object of the invention is tqprovide an improvement by designing an engine of 45 the above mentioned kind so that the ratio: piston' diameter to piston stroke is reduced to 1:4 or less with respect to the usual ratio of approximately 1:3, which may be achieved by making the stroke of each piston of the twin cylinders about 1 times as great as its diameter.

A form of execution of the invention is shown by way of example in the appended drawing, in

. which Figure 1 is a sectional view of an internal 55 combustion engine with a twin cylinder according to the invention through the middle of the cylinder, all the parts which are not essential for the invention being left away.

Figures 2 to 5 are diagrammatical views showing the different sizes of the scavenging and charging angles for different length ratios for the connecting rods.

Figure 6 is a diagrammatical view corresponding to Figure 4 but with this difference that the middles of the cylinders are unequally spaced from the middle of the crank shaft axis.

Figure '1 is a diagrammatical view correspond ing to Figure 4 but;with this diflerence that the middles of the cylinders in Figure '7 are at a smaller distance from the crank shaft axis than in Figure 4.

Figure 8 is the same figure as Figure l in opposition to Figure 9, in which the ratio: piston diameter to piston stroke has the usual value of approximately 1:3 in the whole.

In Figure 1 both two cylinders in and Ii have the common chamber of combustion l2. The cylinders l0 and II are enclosed in a common jacket l3, which comprises, in its upper part, the head H with an aperture I 5 for inserting the spark plug (not shown) which eventually has to be inserted there, and to the lower part of which the crank case is adapted in the usual manner.. In the cylinders l9 and II are slidably mounted the pistons l1 and I9 which are operatively connected with the crank pin 2| through the connecting rods l9 and 29. '22 is the axis of the crank shaft, not shown, and 23 is the crank circle. 24 is an admission port in the cylinder "I, through 'which the fresh mixture may beintroduced into the cylinder through any suitable means, not shown, and 25 is an exhaust port in the cylinder l I, through which the burnt gases may escape into the atmosphere. 26 is the edge of the piston I! which may free and close the admission port and 21 is the edge of the piston III which can free and close the exhaust port when the pistons reciprocate through the movement of the crank pin 2| on the'circle 23.

28 is the radius of the crank circle 23 on which the middle of the crank pin is, when the edge 21 begins to uncover the exhaust port 25; 29 is the radius corresponding to the opening of the admission port 24 through the edge 26 and 99 and 9| are the radii which correspond to the closure of the openings 25 and 24 respectively. The radius 22 corresponds to the lowest position of the crank pin 2|.

In the range"of the angle alpha between 28 and 29 there takes place thus only an exhaust of the burnt gases; in the range of the angle beta between 29 and 90 the scavenging takes place through fresh mixture simultaneously entering through the opening 24, while in the range of the angle gamma between 30 and SI there is only an introduction of mixture into the cylinder-and the supercharging takes place.

As shown, in Figure 1 the exhaust connecting rod 20 is longer thanthe admission connecting rod l9 and in the example shown the relation is Figures 1 to 5 the values of the angle alpha between the radii 28 and 29 and of the angle delta between the radii 29 and 32 are the same, so that the openng of the exhaust takes place 50 and the opening of the admission 30 in advance of the lowest position of the crank. Thus, the angle alpha has a value of 20 and the angle delta has a value of 30. The middles of the cylinders are disclosed at I9 and 20' In Figures 6 and 7 the length relations between the two piston rods 20!) and I9!) are the same as in Figure 4, but in Figure 6 the middles of the cylinders are differently spaced from the crank shaft axis, while in Figure 7 the distance between the'cylinder middles is smaller than in Figure 4 in order to show also the influence of this variation.

The resulting relations are thus the following ones:

Therefore, the more di'flferent from another the lengths of both rods l9 and 20 are made within certain limits, the greater will be the supercharging angle which can be obtained under substantially similar conditions and particularly with equal time-sections for admission and exhaust. On the other hand, a relative increase of the exhaust piston rod 20 will entail an increase of the scavenging angle beta. An increase of the scavenging angle may also be obtained by arranging the middle of the exhaust cylinder ll nearer to the crank shaft axis 22 than the middle of the admission cylinder 10, or by reducing the distance of the middles of the cylinders l9 and II from each other;

Comparing then for instance the arrangements according to Figures 1 and 5, there will be seenthat for the same charging pressure of the mixture and the-same time-sections for admission and exhaust, the supercharging will bealso approximately the same for all speeds, because the supercharging angles are also approximately the same in both cases. But since the scavengingangle in Figure 5 is smaller than in Figure 1, in the engine shown in Figure 5 gases of the mixture will be able to escape through the ex haust, which is still open, only at speeds which are lower than the speeds at which gases of. the mixture may already escape in the case of Figure 1. On the other hand, an increase of the supercharging angle through a relative diminution of the length of the admission piston rod with respect to the exhaust piston. rod, as for instance according to Figure 3 with respect to Figure 1, will be preferable if it is desired, above all, to reduce the power consumption of the device for pressing the mixture into the cylinder.

In Figure 8, which correspondsto Figure l, the diameters d of the pistons ,are smaller than the diameters d ,of the piston in Figure 9, while the crank circle 23 in Figure 8'is greater. than in Figure 9. Therefore, the way up which the gases of the mixture have to travel over from the admission port 24 is longer than 10'. Therefore if it is necessary, for some reason, to have 5 a great scavenging angle, it will be well to make the engine with a long stroke (Figure 1 or 8) contrary to the usual engine with a short stroke according to Figure 9, in which the ratio: diameter d? to the whole stroke of both pistons I1 and ll does not exceed 1:3. Then, for the same pressure of the mixture, the gases oi said mixture reach again the exhaust port, which is not yet entirely closed, at speeds which are lower than they would in the engine with a short stroke as in Figure 9, and it is thus possible to avoid losses oi fresh gases with or without supercharging.

But it is thus possible to obtain a greater power with a greater commercial efliciency which is thus profitable to the acceleration capacity of, for 0 instance, a motor vehicle driven by the engine. For this purpose it has been found convenient to make theratio between the -whole piston stroke, that is the sum 01 the strokes of both pistons, to the piston diameter not smaller than 5 4:1 per se or in combination with piston rods of. a convenient length.

Many possibilities oi changes will be evident ior those skilled in the art. More particularly, the various numerical valueslhave been given only by way of examples and it is notintended to limit the scope oi the invention to said values, reference being had, in this respect, to the appended claims.

I claim: 1. In a two stroke internal combustion engine of the u-shape kind with twin cylinders connected together through a. common combustion chamber, a crank shaft having crank pins, one of said cylinders having an admission port for the an exhaust port for the burnt Eases, means for controlling the opening and closure of the admission and exhaust ports, including pistons having connecting rods pivotaliy connected with, the same crank pin, the piston rod of the piston (or the cylinder with the exhaust port having a ter length than the piston rode! the piston for the cylinder with the admission port. 1 50 2. In a two stroke internal combustion engine of the U-shape kind with twin cylinders connected together through a common combustion chamber, one oi said'cylinders having an admission port for the scavenging and charging 55 mixture and the other an exhaust port for the burnt gases, pistons in the cylinders controlling the admission and exhaust ports, piston rods connected with the pistons and acting on the crank shaft in the same size crank circles, the m piston rod of the piston tor the cylinder with the exhaust port having a greater length then the piston rod oi the piston for the cylinder with the admission port, and the middle line of one of the cylinders being at a greater distance from scavenging and charging mixture and the other the crankshaft axis than the middle line of the other cylinder.

3. In a two stroke internal combustion engine of the U-shape kind with twin cylinders connected together through a common combustion 5 chamber, one of said cylinders having an admission port for the scavenging and charging mix ture and the other an exhaust port for the burnt gases, pistons in the cylinders controlling the admission and exhaust ports, piston rods connected with the pistons and acting on the crank shaft in the same size crank circles, the piston rod of the piston for the cylinder with the exhaust port having a difl'erent length than the piston rod or the piston for the cylinder with the admission port,and the middle lineoi one of the cylinders being at a greater distance from the crank shaft axis than the middle line or the other cylinder. I

4. In a two stroke internal combustion en ine or the U-shape kind with twin parallel cylinders connected together through a common combustion chamber, one of said cylinders having an admission port for introducing the scavenging and charging mixture to both cylinders and the other having an exhaust port for discharging the burnt gases i'rom,both cylinders, pistons oi the same diameter in the cylinders controllingthe admission and exhaust ports, a shaft having a crank pin, and piston rods oi diiIerent lengths so 'pivotally mounted about the axis or the crank.

pin, the ratiobetween the sum of the strokes oi. both pistons to the diameter of the pistons being not smaller than 4:1.

5. In a two stroke internal combustion engine of. the U-shape kind with twin cylinders connected together through a common combustion chamber, one of said cylinders having an admission port for the scavenging and charging.

and the other an exhaust port for the 40 burntgasea pistons in the cylinders, connecting rods pivotally connected with the pistons and the. same crank tor controlling the admission and exhaust ports, the piston rode! the piston for the cylinder with the exhaust port having a greater length thanthe pistonrod oi the piston for the cylinder with-theadmission portithe ratio:- between the sum of the strokes of both pistons to the diameter of the pistons being not smaller than 4:1

- 6.1aatwocycleinternelcombustionengine having a crank shaft, a pair of parallel cylinders connecttescll by a common combustion chamber, the axes o d cylindersbeing on opposite I the crank shalt axis,'one of said cylindefs a ing an intake P rt. the other of said cylinders having an exhaust port, a shaft havinga crank pin, pistons in said cylinders for controlling said ports, and connecting rods of unequallengths connected to said pistons and pivotelly mounted about the axis of said crank pin, the longer of said rods being connected to the piston controlling the exhaust port.

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